1. Field of the Invention
The vehicle of this invention is a fork lift truck of a generally tricycle type having widely spaced apart forwardly extending drive wheels and a centrally disposed rear caster wheel. All of the wheels are equipped with pneumatic tires thus enabling the lift truck to move and be used over rough ground. However, at times the flotation of such a tricycle vehicle gets bogged down in muddy terrain. It is at these times that the present invention comes into use. An auxiliary drive wheel is provided outwardly of and on both sides of the rear caster wheel. These auxiliary drive wheels are arranged on the vehicle for vertical shifting movement from an up inoperative position to a down ground engaging operative position. When the auxiliary wheels are powered downwardly the rear caster wheel is raised from the ground and the lift truck becomes a four wheel drive vehicle with power and flotation to go through any ground conditions.
2. Description of the Prior Art
A preliminary patent search was conducted and the following patents were believed to have some pertinence relative to patentability.
The U. S. patent to Collins No. 1,742,636 employs vertically movable rollers disposed at right angles to the regular wheels of an automobile to permit ease of parking. When the rollers are lowered the automobile may move sideways into a narrow parking space.
The U. S. patent to Clements No. 2,864,625 shows swingable wheels which can be lowered to ground engaging position to give stability to a boom carried by the vehicle.
The U. S. patent to Prichard No. 3,191,963 discloses a swingable auxiliary wheel or wheels to distribute the load the vehicle is carrying over a greater number of wheels than normally.
The U. S. patent to Matsukata No. 3,502,165 shows optional pairs of rear wheels. When one pair of rear wheels is down in ground engaging position the vehicle is operated by a gasoline engine, and when the other pair of rear wheels is down in ground engaging position the vehicle is operated by electricity.
The U. S. patent to Williams No. 3,826,322 discloses a device to ease parking and is similar to the Collins patent discussed above. The differences appear to be in the means for lowering and raising the auxiliary wheels and the auxilieary wheels of Williams are larger in diameter than the rollers employed by Collins.
The U. S. patent to Greppi No. 3,850,472 describes an automobile comprised of two major parts which are hinged at their tops. Thus the automobile may be condensed or spread out longitudinally as desired. When condensed the vehicle fits into smaller parking spaces.
The U. S. patent to Anderson No. 4,063,611 shows a vehicle in which air or gas cushion forces are used for hull suspension or flotation and downwardly movable wheels are used for propulsion and/or steering.
It is obvious other vehicles have employed downwardly shifting wheels, but no one has previously converted a tricycle type vehicle to a four wheel vehicle, and not converted a two wheel drive vehicle to a four wheel drive vehicle by lowering auxiliary drive wheels flanking the sides of a centrally disposed non-driven caster wheel at the rear of the vehicle.